Experimental investigation of phase equilibrium in the Gd2O3 - NiO, NiO - ZrO2 and Gd2O3 - NiO - ZrO2 systems at 1773 K and 1573 K

A comprehensive phase equilibria investigation was conducted in the Gd 2 O 3 - NiO - ZrO 2 system and its binary subsystems (Gd 2 O 3 - NiO and NiO - ZrO 2 ) at 1773 K and 1573 K via solid-phase reaction approach. The NiO - ZrO 2 binary system was initially studied between 1373 K and 1773 K, and the decreased martensitic transition temperatures (1236 K) were determined, confirming Ni 2+ stabilization of t'-ZrO 2 . Homogeneity ranges for Gd 3+ and Zr 4+ in NiO demonstrated minimal temperature dependence. No intermetallic compounds were observed in these subsystems, but a new ternary compound NiO·ZrO 2 ·3Gd 2 O 3 (τ) was identified in the ternary system. Isothermal phase equilibria of the ternary system revealed extended three-phase regions (T + Fl + Hl, Fl + C+ τ etc.) and solubility variations with temperature. Based on experimental data and literature assessments, phase diagrams for the subsystems and ternary isothermal sections were constructed with high reliability.